| 摘要 |
PURPOSE:To block a noise or an impact noise and to maintain the audibility of a speech voice by providing a filter to extract the speech voice frequency band component, and providing a level limitation circuit to limit the level of an output signal from a microphone amplifier. CONSTITUTION:An electrical signal outputted from the microphone MK is amplified in the microphone amplifier MA, then inputted to the filter FL. The filter FL passes only the speech voice in the pass band of 600-1500Hz, but blocks other frequencies, i.e., noises. A speech voice passed through the filter FL is amplified by a headphone amplifier HA, then supplied to two speakers SP1, SP2, and the speech voice is emitted as a physical voice onto the left and right ear pads of an earmuff. Meanwhile, the output signal level of the amplifier MA is detected by the level limitation circuit LM, and corresponding to the high and low of the output level, the input level of the amplifier MA is varied high and low. Therefore, an impact noise that exceeds a prescribed level can be blocked. |
